The image is composed of a large number of pixels arranging according to specified matrix, LED display panel is composed of many LED display modules, and LED display module is composed of several pixels that independently form the smallest element of LED display panel in structure. Recently, the most common 3 types of LED display modules are as follows:
1. Matrix module structure: LEDs are regularly arranged in a matrix on the printed board. Whilst the back of printed board is vertically inserted into with the several metal needle-type pins, the front of printed board is covered with the injection molding unit. All luminous points of every pixel on said injection molding unit are equipped with reflecting cavities whose internal diameters are smaller than their external diameters in order to increase the luminance. A LED matrix display module is formed when the matrix module is filled with epoxy resin during fabrication.
2. Surface mount lamps structure: Surface mount lamps structure is also called as SMD type structure, whose each pixel is an independently filling SMD type LED containing luminous LED chip, metallic pins and reflecting cavity. Each pixel arranged in matrix is soldered on the matrix printed board with special soldering technology to form a LED display module.
3. The display module of luminous pixel composed of LED single lamp. As to a LED matrix module, when it is observed from the front of LED display panel, the inside section of the reflecting cavity of each pixel dot (close to the printed board) and the outside section (close to the display panel surface) are two cavities of different diameters, that look like a round disk being smaller inside, and bigger outside, the outside is acted as the luminous surface of the pixel dot. Because the manufacturing cost of the LED display panel is nearly proportional to the quantity of pixels, the resolution of the display panel is generally so designed as to reach the critical state of display effect that human eyes can accept. Therefore, the unavoidable black areas are formed between the luminous areas of each pixel. The influence of the black area on the display can be described as luminance area ratio (that is also called as fill factor). Luminance area ratio is the proportion between the luminous areas of each pixel on the display panel and the occupation area of each pixel on the display panel. The bigger the luminance area ratio is, the smaller the black area is and the better display effect is.
TCO has taken the pixel resolution or luminance area ratio in the display industry and flat display field as an important index to measure the display quality. According to the stipulation of TCO'99 Standard, luminance area ratio must be not less than 0.5. Moreover the pixel density must be not less than 30 pixel/degree as stipulated in TCO'03.
(TCO stems from Swedish language “Tianstemannens Centralorganlsatlon”, English translation is “The Swedish Confederation of Professional Employees”, which is called “SCPE” for short. With the issue of TCO Development of safety and environment protection standard for computer equipment in 1992, TCO Development has been widely recognized all over the world. Recently TCO Development is one of the most common developments generally acknowledged in the display industry.)
All display panels have the defects of small luminous area and bigger black area for all display module structures, either dot matrix structure, LED single diode structure or SMD structure in LED display panel field, therefore, the luminance area ratios are lower. As per estimation, the average luminance area ratio of a SMD type full color display panel with 10 mm pitch, 2.2 mm diameter of each luminous point is only 0.076; maximum luminance area ratio is just 0.11 as well. Even though the luminance area ratio of matrix structure is much higher than that of SMD structure, its luminance area ratio is not high. The sample of LED cluster D5 mm is taken as follows:
Common pitch 7.525 mm, the luminance area ratio:
                    π        ⁡                  (                      5            /            2                    )                    2              7.525      2        =  0.34
Compact pitch 6.33 mm, the luminance area ratio:
                    π        ⁡                  (                      5            /            2                    )                    2              6.33      2        =  0.49
All the above values are lower than a commonly recognized value of 0.5.